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Thread: Hubs with built-in tripod joint

  1. #1

    Hubs with built-in tripod joint

    Hi guys,

    My name is Josh and I'm the president of Boston University Racing. This post is to share my design and manufacturing of our rear hubs, which have built-in tripod joints.

    Any feedback, questions or concerns are welcome.

    The idea behind the design is to eliminate the need for additional fastening components, separate tripod housing and to push our team a little. This is our first year and we have never built a car, so built-in tripod joints was an ambitious decision, in my opinion. The system uses Taylor Race (thanks Scotty) nickel inserts as well as their tripod. Pictures can be seen below

    IMG_3758.jpgIMG_3876.jpgIMG_3894.jpgIMG_3920.jpg


    Josh
    Attached Images
    Joshua Byington

    Boston University Racing

  2. #2
    What do you want to ask?

    How are you attaching your tripod boot? I have a personal issue with FSAE cars using monstrous 4WD spec CV boots. We use Tie rod dust covers, similar to this:
    http://www.ebay.com.au/itm/te-8-repl...a6ca70f&_uhb=1

    We then make a custom flange for them to slip over. Makes for a neat, easy and cheap FSAE sized CV boot.

    12091377_10208125042828230_461654212395868568_o (1).jpg
    UQ Racing

  3. #3
    Senior Member
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    1,688
    Josh,

    Sorry, but NOT good IMO. Many weak points...

    What bearings are you using, and what are your planned tolerances and preloads for the bearing mounting surfaces?

    Z

  4. #4
    Mitchell, thanks for your boot feedback. I agree most FSAE boys are oversized and are not necessary. I'll consider your link.

    Z, no problem, I'm here to learn and make next year's team and car as good as they can be. Can you specify what issues you think my design has? We are using SKF DGBB with a light press on the spindle and a slight slip in our uprights. Per SKF recommendation, I plan to machine an inner race spacer to snug up against.

    Thank you both for your help,
    Josh
    Joshua Byington

    Boston University Racing

  5. #5
    Quote Originally Posted by Z View Post

    Sorry, but NOT good IMO. Many weak points...

    Z

    Sorry Joshkb, sometimes Z will write you a personal textbook to help, and sometimes you get this.


    I think they look fine, and you seem to be well capable of manufacturing it. Neat use of the 3d printing. Some things I notice, overall it seems fine:

    1) you could add some webbing in the upright to help torsional stiffness. better to build a closed shape for that in general
    2) the brake hat could be relieved between bobbins if you only have 4, similar to the brake disks
    3) those bearings - can't tell what type they are, but in general you can't preload them much - will need to add positive retention to the spindle nut anyway to pass tech I think
    4) what keeps the inserts from sliding out? friction? Wouldn't trust that. seems your cad shows holes drilled for a faceplate there?
    5) the step/ridge that presses on the outboard bearing may be too small diameter - sometimes large bearings have a decent radius/chamfer that might try to wedge onto this.
    6) brake hat could have larger radii at the base to reduce stress without much change in weight. FEA may not show it but in real life you might have an axial load there


    less useful:
    a) the CAD for the wheel might be improved, just to be careful about space
    b) same note, based on experience you may want to ensure >0.25" clearance between the wheel shells and components to account for possible deflection
    c) brake caliper mounting may be convenient there, but I expect it isn't optimal for loading. Check out how the bearing forces change during braking as you change the location of the brake caliper the bearing forces change
    d) is the material between the tulip housing and the hub empty? Could you bore it out from the outboard side?
    e) do you have boots that fit the nut? As Mitchell suggests, there are better options. The ones that fit those nuts are surprisingly heavy
    Austin G.
    Tech. Director of APEX Pro LLC
    Auburn University FSAE
    War Eagle Motorsports
    Chief Chassis Engineer 2013
    Vehicle Dynamics 2010-2012

  6. #6
    Thanks Goost, very helpful. Let me try to address your comments:

    1 - The uprights havent been made and I agree, the added weight wouldnt be much so why not go stronger?

    2 - The idea here is that the aluminum surface may bet work out eventually, which I assume will happen before the rest of the hub has minished its service life. In that case, we can rotate 45 degrees and have fresh surfaces. I just don't think our team is at a point where we should spend a whole lot of time on weight reduction. Remember, this is our first car..ever.

    3 - They are SKF 61816 DGBB 80x100x10..can you explain what you mean?

    4 - The inserts have a very tight press fit which we were able to achieve without temperature difference due to the inserts not being closed, so they can flex a bit when clamped on. They are very tight. I guess time will tell on that one...

    5 - This is a good point, as these bearings do have a fairly large radius. Hopwever, I am following SKF reccomendartions for this diameter, so I will leave that alone.

    6 - We are running 10" wheels, which makes the whole brake systrem a challenge. Between an 80mm spindle to accomodate the tripod housing and inserts, as well as the radial clearance required between our calipers and inner wheel, we have less than a millimeter to play with there. I wish we could fit larger radii.

    a,b - We have roughly 5mm clearance from components to wheel, so a little tighter than you reccomend, but still comfortable, I believe.

    c - Is this a front caliper vs. rear caliper comment, or regarding the deflection in outer race bearing housing induced from braking force at caliper connections? Let me know..

    d - I bored 100mm from the outboard side and saved ~ 1.6 lbs, I'd have to check the model weight. I think that'
    s what you're getting at

    e - My appologies, we are actually making custom aluminum nuts from the material we bandsawed off of the blanks to make these hubs, so these are not the final nuts.

    Thanks for your helpful comments, Austin.

    Josh
    Joshua Byington

    Boston University Racing

  7. #7
    Thanks Josh ,,

    Nice work . I will second Mr. Goost on some type of retaining device on the inserts. A little heat in the housing and your tight press assumtion just cost you endurance..The insert you have in the model needs to be flipped around . and the pin used to keep it from
    rotating in the housing .
    scotty
    Taylor Race
    scotty@taylor-race.com
    taylor-race.com

  8. #8
    Josh,

    Don't let anyone (Z) on this forum scare you from pursuing an idea just because they think it's a bad idea..... We ran one piece aluminum rear hub/tripods from 2011 till I graduated in 2014 and never had a single problem with them wearing out or getting excessively sloppy. That was on both 4-cylinder big power, little torque and 1-cylinder big torque, little power engines.

    To speak to their potential reliability; when I graduated in 2014, our 2012 car had about 2100 miles on it and it's still driving.

    In summary, with proper design and manufacturing you can absolutely make it work....... Even if Z thinks that it is "NOT a good idea"


    Cheers!
    ___________________________

    Zips Racing 2009-2014
    Jorts and Tank-top model 2013-2014

  9. #9
    2 - The idea here is that the aluminum surface may bet work out eventually, which I assume will happen before the rest of the hub has minished its service life. In that case, we can rotate 45 degrees and have fresh surfaces. I just don't think our team is at a point where we should spend a whole lot of time on weight reduction. Remember, this is our first car..ever.
    Neat idea. Personally never seen that surface fail, except once when that was the least of the issues compared to everything else that broke...

    3 - They are SKF 61816 DGBB 80x100x10..can you explain what you mean?
    If I recall DGBB are OK for axial loads, maybe not as good as an angular contact version?
    Anyway, I meant that the desired pre-load for the bearings is probably lower than desired to keep the big jam nut in place, so to keep the nut from walking away it needs some type of secondary retention, a pin or something.
    That nut is also considered a "suspension fastener" so it needs a positive locking mechanism anyway to pass technical inspection (since you are machining your own it might be especially scrutinized).

    4 - The inserts have a very tight press fit which we were able to achieve without temperature difference due to the inserts not being closed, so they can flex a bit when clamped on. They are very tight. I guess time will tell on that one...
    As Scotty says, I wouldn't trust the press fit. Tripod bearings can generate some odd loads, even pulling on the inserts even though it seems like they should just roll smoothly.
    A plate on the spindle face, or a pin as he says may be useful. Also, if the inserts are cylindrical you may want a pin or something else to keep them from rotating.

    c - Is this a front caliper vs. rear caliper comment, or regarding the deflection in outer race bearing housing induced from braking force at caliper connections? Let me know..
    Hm, I'm not thinking about deflection.
    So, as you rotate the location of the caliper around the spindle, the couple between the bearing and the brake caliper is the same magnitude during braking - BUT the bearing's force component changes direction.
    You can use this force to offset bearing loads during braking. Perhaps reduce the total bearing load after you sum forces from from the vehicle weight, lateral force, longitudinal force, AND this caliper/bearing couple.
    (Example| during straight-line braking, assume the weight transfer is large compared to longitudinal force, no scrub radius or KPI, and look at front uprights:
    If the caliper is on the back of the upright, then the vertical forces from the weight transfer and caliper/bearing couple sum "in opposite directions" to create a smaller total bearing load.
    If the caliper is on the front of the upright, then they sum in the same direction - creating a larger total bearing load.
    For your design you consider braking and cornering (which typically produces the largest bearing loads) and your specific upright geometry, so the ideal solution changes.
    For similar reasons, the ideal bearing location is not centered in the wheel, rather it is slightly inboard. but your upright is past that stage now I think.)

    d - I bored 100mm from the outboard side and saved ~ 1.6 lbs, I'd have to check the model weight. I think that'
    s what you're getting at
    Exactly! Big radius in the bottom of that pocket?


    Hope it helps!
    Austin G.
    Tech. Director of APEX Pro LLC
    Auburn University FSAE
    War Eagle Motorsports
    Chief Chassis Engineer 2013
    Vehicle Dynamics 2010-2012

  10. #10
    Senior Member
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    Oct 2007
    Location
    Bolton, CT
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    143
    Neat idea. Personally never seen that surface fail, except once when that was the least of the issues compared to everything else that broke...
    You might want to machine those before you assemble if that's something you are worried about. I'd be a shame to need to disassemble just to make a few pockets.

    If I recall DGBB are OK for axial loads, maybe not as good as an angular contact version?
    Anyway, I meant that the desired pre-load for the bearings is probably lower than desired to keep the big jam nut in place, so to keep the nut from walking away it needs some type of secondary retention, a pin or something.
    That nut is also considered a "suspension fastener" so it needs a positive locking mechanism anyway to pass technical inspection (since you are machining your own it might be especially scrutinized).
    Austin makes a good point here. You definitely need a positive retention mechanism (pin, etc.) for tech and to make sure it doesn't back out with the low axial loads.

    Just so you know, we have used this bearing with good success. We calculated it's lifetime to be a little short for the application and assumed we would need to replace it, but in 3 years we haven't had a bearing failure. Note that after a full competition and training season we have seen some bearing getting a little rough. Our design focused more on getting the radial preload correct since our bearings are not axially constrained (probably not the best design, but it works well enough).
    Jim
    "Old guy #1" at UCONN Racing

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